To find the greatest common factor (GCF) of the expression \(42m - 28n\), we first need to identify the GCF of the coefficients 42 and 28.
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Find the factors of 42:
- 42 = 1, 2, 3, 6, 7, 14, 21, 42
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Find the factors of 28:
- 28 = 1, 2, 4, 7, 14, 28
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Identify the greatest common factor:
The common factors of 42 and 28 are 1, 2, 7, and 14. The greatest of these is 14.
Thus, the GCF of \(42m - 28n\) is 14.
Therefore, the correct response is: 14.